The natural vibration a product experiences under the actual working condition is the composite vibration in the triaxial directions of X, Y and Z. In order to actually show the vibration resistance of the product and simulate the natural vibration condition, a triaxial vibration composite testing apparatus is finally designed after many years of attempt.
Many kinds of triaxial vibration composite testing apparatuses have been disclosed so far at home and abroad, which generally have the following structure: There is a working tabletop 1 for receiving a test piece; a vibration generator 2 is positioned in the triaxial directions of X, Y and Z, respectively, with the working tabletop 1 as the datum; and the working tabletop 1 is connected with each of the vibration generators 2 through an axial vibration transmission mechanism. The axial vibration transmission mechanism is used to constitute a rigid connection in this axial direction and transmit the exciting force of the vibration generator 2 to the working tabletop 1, while to decouple in the other biaxial directions. Among the prior various triaxial vibration composite apparatuses are the two representative ones as below:
1. Cross-linear-guide triaxial vibration composite testing apparatus. See an application for a patent for an invention titled “Connection Mechanism of Three-Way Exciting Platform of Vibration Table” disclosed in the Chinese Patent Publication No. 101241036A on Aug. 13, 2008. The structure is as shown in FIGS. 1 and 2. The force transmission mechanisms in its triaxial directions of X, Y and Z (i.e. the axial vibration transmission mechanisms) are all a cross linear guide pair 3, which is specifically composed of a slide block 4 as well as a transverse guide 5 and a longitudinal guide 6 in sliding connection with the upper and the lower end planes of the slide block, respectively. This triaxial vibration composite testing apparatus is simple in structure because the axial vibration transmission mechanism adopts the cross linear guide pair 3, and low in manufacturing cost because the cross linear guide pair 3 can be bought. However, this apparatus has the following shortcomings:
1) The motion mass is very different in various axial directions.
2) There are so many connection joints on the force transmission path from the vibration generator 2 to the working tabletop 1 that the vibration frequency response characteristic is affected, and especially its vibration response characteristic in the perpendicular Z axial direction is very poor, which makes it applicable to the low frequency vibration test.
2. Hydrostatic triaxial vibration composite testing apparatus. See U.S. Pat. No. 5,549,005. The structure is as shown in FIG. 3. The working tabletop 1 is in fixed connection below with a middle cube 7, at the left, right, front and back of which as well as below which is positioned a pressure application plate 8. Each of the pressure application plates 8 fits the middle cube 7 with a plane gap, each of which is filled with the high pressure oil to form a hydrostatic oil film 9, thus constituting a triaxial hydrostatic plane bearing structure. Each of the pressure application plates 8 is in fixed connection outside with a connection shaft 10, through which the vibration generators 2 in various axial directions are connected. In short, this triaxial vibration composite testing apparatus uses the hydrostatic plane bearing as the axial vibration transmission mechanism to connect the working tabletop 1 to the uniaxial vibration generator 2. This triaxial vibration composite testing apparatus is light in weight due to fewer motion parts in each of the axial directions, wide in the vibration frequency range with the upper working frequency limit up to over 1,000,000 Hz, and good in the frequency response characteristic. However, it still has the following shortcomings:
1) Manufacture. Because of the hydrostatic bearing structure in all the triaxial directions, the structure is more complicated, and each of the fit planes is high in requirement and hard to be processed, which increases the manufacturing cost.
2) Vibration test performance. The middle cube 7 of a certain height needs to be positioned below the working tabletop 1 to facilitate arranging the pressure application plate 8, which then increases the distance from the working tabletop 1 to the vibration generator 2 in the perpendicular axial direction (that is, the working tabletop 1 is lifted up), thus affecting the entire rigidity to some extent; the middle cube 7 and several pressure application plates 8 need to be positioned below the working tabletop 1, which increases the mass of the motion part; the rigidity is poor and the mass of the motion part big, which directly limit the further increase in the working frequency; moreover, lifting the working tabletop 1 also causes the antioverturning moment capacity to decrease.